Many contaminated DOE sites are located in arid regions where depth to groundwater is significant and/or contaminants were discharged into a vadose zone through which transport to the groundwater table is dominated by unsteady, unsaturated groundwater flow. The absence of an effective means to monitor vadose zone moisture content in profile has been a persistent impediment to developing and calibrating transport models critical to site management, and to monitoring the dynamic moisture conditions that have a controlling influence on contaminant transport in the vadose zone. We propose to research an in situ monitoring concept that may provide the ability to spatially resolve volumetric soil moisture in profile (as well as water table elevation), thus enabling substantial improvements in the state-of-the-art of model development, verification, and long-term monitoring crucial to effective site management and remediation. Preliminary experimental data in a limited range of conditions establish the feasibility of the approach, which combines advances in the processing of time domain reflectometry (TDR) data with innovations in the physical sensing apparatus, thus enabling the acquisition of spatially resolved soil moisture profiles. The sensor will be suitable for installation into boreholes created by both direct push and drilling methods, using a flexible borehole lining technology that is well-established in environmental site characterization and monitoring, to ensure intimate contact with the formation and suppress the potential for hydrologic short-circuiting through the borehole. Phase 1 will include laboratory to research performance of the method in a range of soil types and at varying pore water salinities, and will also research the suitability of commercial flex circuit manufacturing technology to produce waveguides of the physical characteristics required to maximize precision, accuracy, durability, and achievable length of continuous measurement profile. Phase I will also research issues associated with design for deployability using flexible borehole liner technology and will produce prototype PRISMS for later emplacement at a DOE IFRC site, where time series data will be acquired from PRISMS and compared to periodic neutron logging of nearby boreholes. Phase 2 will research in situ performance by producing and installing prototypes at a DOE test site, investigate design for manufacturability, rigorously assess pathways to commercialization, and evaluate full lifecycle costs and benefits of the technology if fully commercialized. Commercial Applications and Other Benefits: In addition to the public benefit of improved environmental site management, future applications of the technology, if developed through Phase 2 and beyond, include monitoring for advance warning of landslide-producing moisture conditions, climate research and permafrost monitoring, and sensing ice formation on aircraft wings, all of which have clear public safety benefits.